JP2018147528A - Hologram recording and reproducing method and hologram recording and reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hologram recording and reproducing device and a hologram recording and reproducing method capable of high-speed recording and reproducing.SOLUTION: In the present invention, a spherical wave is used as reference light, and in a state where a recording medium is stationary, by changing an incident direction of the reference light on the recording medium using reference light incident angle changing means to multiple record a plurality of holograms in the same position in the recording medium, after a multi hologram is recorded, in a state where one of an optical head radiating signal light and the reference light and the recording medium is relatively shifted in one direction with respect to the other, a new multi hologram is recorded so as to be overlapped in a portion of a recording area where the multi hologram is already recorded.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a hologram recording / reproducing apparatus and a hologram recording / reproducing method. More particularly, the present invention relates to a hologram recording / reproducing apparatus and a hologram recording / reproducing method capable of performing high-speed recording / reproducing when a large-capacity optical memory is configured by multiplexly recording a two-dimensional digital bit pattern as a hologram on a recording medium.

  2. Description of the Related Art Conventionally, hologram recording / reproducing apparatuses that record and reproduce digital information two-dimensionally using holograms have been proposed. In a hologram recording / reproducing apparatus, signal light carrying digital information (data information) modulated by a spatial light modulator composed of a plurality of pixels and the signal light and coherent reference light interfere with each other in a recording medium. The resulting interference fringes are recorded as a hologram. In addition, when reproducing a hologram recorded on a recording medium, diffracted light is generated by irradiating the hologram with reference light used for recording, and is recorded as a hologram on an image pickup device such as a CCD. An image of digital information is formed.

  As a hologram multiplex recording method, for example, an angle multiplex recording method, a spherical reference light shift multiplex recording method using a spherical wave (hereinafter also referred to as “spherical reference light”) as reference light, and the like are known. (For example, refer to Patent Document 1).

  In the angle multiplex recording method, the incident angle of the reference light (for example, plane wave) with respect to the recording medium is minutely changed, and multiplex recording of the hologram is performed at the same location on the recording medium. When the thickness of the recording medium is thick (specifically, 1 mm or more), the Bragg diffraction condition becomes severer in angle, and when the angle is about 0.1 °, the Bragg diffraction angle condition is removed and reading is impossible. . Using this principle, hundreds of holograms are multiplexed and recorded at the same location on the recording medium.

  In the spherical reference beam shift multiplex recording system, if the recording medium on which the hologram is recorded is shifted by a slight distance in one direction along the surface of the recording medium, the relationship between the wave vectors deviates from the Bragg diffraction condition. Thus, it becomes impossible to reproduce the already recorded hologram, and it becomes possible to record a new hologram in a state where a part of the recording area overlaps the recording area of the already recorded hologram. Here, the distance between adjacent holograms, that is, the shift amount is about 10 μm.

JP 2014-098797 A

  Thus, as a technique for controlling the relative position between a light beam (signal light and reference light) and a recording medium in a hologram recording / reproducing apparatus employing a conventional spherical reference light shift multiplex recording method, for example, signal light and reference light The optical mechanism for irradiating the recording medium is not moved, and a method of accessing the recording medium by biaxial movement and rotation is adopted. In this method, the irradiation position of the signal light from the optical mechanism and the reference light on the recording medium is fixed, the recording medium is moved and then stopped, a hologram is formed in this state, and the recording medium is moved again. The process of stopping and forming a new hologram is repeated (stop-and-go method).

In such a method, in order to increase the data transfer speed during recording or reproduction, it is necessary to control the moving stage on which the recording medium is mounted at high speed. For example, assuming that one hologram for a recording medium can be recorded in a recording time of 1 ms, for example, and the recording medium is moved by a distance of 10 μm, which is a shift amount, in 50 ms, the time required for one recording sequence is 51 ms. It becomes. Therefore, the transfer rate at the time of recording is limited to 20 Mbps or less. Actually, when stop-and-go that moves a distance of 10 μm in a time of 50 ms is repeated, vibration occurs in the recording medium, and normal recording of the hologram becomes difficult.
In order to avoid the occurrence of such a problem, it is necessary to increase the moving time to 50 ms or more, so the transfer speed during recording is greatly reduced, and the effectiveness of the shift multiplex recording system is greatly increased. You will lose. That is, when increasing the capacity of the recording information by the shift multiplex recording method, the moving time by the mechanical mechanism is required every time the recording medium is shifted, so that the transfer speed at the time of recording is lowered.

  The present invention has been made based on the above circumstances, and is a hologram recording that enables high-speed recording / reproducing in a hologram recording / reproducing apparatus and hologram recording / reproducing method adopting a spherical reference light shift multiplex recording method. An object is to provide a reproducing apparatus and a hologram recording / reproducing method.

The hologram recording / reproducing method of the present invention multiplex-records a hologram formed by causing signal light carrying data information and reference light to interfere with each other on a recording medium by a shift multiplexing method, and records the hologram on the recording medium on which the hologram is recorded. In the hologram recording / reproducing method for reproducing the data information recorded in the hologram by irradiating the reference light,
Use spherical wave as reference light,
After recording a multi-hologram by changing the incident direction of the reference light with respect to the recording medium by the reference light incident angle changing means and performing multiplex recording at the same location on the recording medium while the recording medium is stationary ,
In a state where one of the optical head that irradiates the signal light and the reference light and one of the recording media is shifted in one direction relative to the other, a part of the recording area of the multi-hologram has already been recorded. Recording is performed in a state where the recording area overlaps the multi-hologram recording area.

  In the hologram recording / reproducing method of the present invention, an acousto-optic element is preferably used as the reference light incident angle changing means.

Furthermore, in the hologram recording / reproducing method of the present invention, the product of the angular interval θ [°] for changing the incident angle of the reference light and the shift amount δ [μm] of the optical head or the recording medium is α [°. .Mu.m], it is preferable that the angle interval .theta. And the shift amount .delta. Are set so that 50.ltoreq..alpha..ltoreq.100.
In such a case, it is preferable that the angular interval θ is set within a range of 1 ° to 10 °, and the shift amount δ is set within a range of 5 μm to 50 μm.

The hologram recording / reproducing apparatus of the present invention multiplex-records a hologram formed by causing interference between signal light carrying data information and reference light on a recording medium by a shift multiplexing method, and also records the hologram on the recording medium on which the hologram is recorded. In a hologram recording / reproducing apparatus for reproducing data information recorded in a hologram by irradiating a reference beam,
An optical head including a signal light irradiation optical system for irradiating the recording medium with signal light and a reference light irradiation optical system for irradiating the recording medium with spherical reference light;
The reference light irradiation optical system includes reference light incident angle changing means for changing the incident direction of the spherical reference light to the recording medium,
In a state where the recording medium is stationary, a plurality of holograms are multiplexed and recorded at the same location on the recording medium by changing the incident direction of the spherical reference light to the recording medium by the reference light incident angle changing means. After being recorded
In a state where one of the optical head and the recording medium is shifted in one direction relative to the other, a new multi-hologram overlaps with a multi-hologram recording area in which a part of the recording area has already been recorded It is recorded by.

  In the hologram recording / reproducing apparatus of the present invention, it is preferable that the reference light incident angle changing means is an acousto-optic element.

Furthermore, in the hologram recording / reproducing apparatus of the present invention, the product of the angular interval θ [°] for changing the incident angle of the reference light and the shift amount δ [μm] of the optical head or the recording medium is α [°. .Mu.m], it is preferable that the angle interval .theta. And the shift amount .delta. Are set so that 50.ltoreq..alpha..ltoreq.100.
In such a case, it is preferable that the angular interval θ is set within a range of 1 ° to 10 °, and the shift amount δ is set within a range of 5 μm to 50 μm.

  In the present invention, after multiple holograms are recorded by changing the incident angle of the reference light with respect to the recording medium and being overwritten at the same location, one of the recording medium and the optical head is relative to the other. In a state shifted relatively in one direction, a new multi-hologram is recorded in a state where a part of the recording area is overlapped with the recording area of the already-recorded multi-hologram, thereby performing multiplex recording of the hologram . For this reason, for example, it is possible to multiplex-record holograms while suppressing the number of stop-and-go operations of the moving mechanism for shifting the recording medium as small as possible. Therefore, according to the present invention, even when shift multiplex recording is performed by shifting the optical head or the recording medium at a moving speed that does not cause vibration, a sufficiently high transfer speed during recording can be obtained. High-speed recording / reproduction is possible.

  In particular, since the incident direction of the reference light with respect to the recording medium is changed by the acousto-optic element, the control of the incident direction of the reference light with respect to the signal light can be performed in a very short time without driving a mechanical mechanism such as movement of the recording medium. In addition, the configuration of the hologram recording / reproducing optical system can be simplified.

  The product α [° · μm] of the angle interval θ [°] for changing the incident angle of the reference light and the shift amount δ [μm] of the optical head or the recording medium is in the range of 50 or more and 100 or less. By setting the size of the angle interval θ and the size of the shift amount δ so as to be equal to each other, the density of information recorded on the recording medium can be increased without causing crosstalk. .

It is a time chart for demonstrating an example of the hologram recording / reproducing method of this invention. It is explanatory drawing which shows the outline | summary of the recording / reproducing method of a hologram. It is the schematic explaining the operation principle of an acousto-optic modulator. It is the schematic explaining the function of an acousto-optic modulator. It is explanatory drawing which shows the mutual relationship of the recording grating | lattice vector of the hologram multiplex-recorded by the hologram recording / reproducing method of this invention. It is explanatory drawing which shows the outline of a structure in an example of the hologram recording / reproducing apparatus of this invention with a recording medium. It is explanatory drawing which shows the outline of the structure in the other example of the hologram recording / reproducing apparatus of this invention with a recording medium.

  Hereinafter, embodiments of the present invention will be described in detail.

  The hologram recording / reproducing method of the present invention uses a spherical wave as reference light, and a plurality of holograms formed by causing signal light and reference light to interfere with each other while the recording medium is stationary is applied to the reference light recording medium. The operation of recording the multi-hologram by changing the incident direction and overwriting the same place on the recording medium is performed by using one of the optical head for irradiating the signal light and the reference light and the recording medium relative to the other. By repeatedly performing the shift in one direction, the recording information is densified. In addition, each hologram is reproduced independently by irradiating a recording medium on which holograms are multiplexed and recorded with reference light.

In the hologram recording / reproducing method of the present invention, a recording medium having any shape such as a disk shape or a card shape may be used. For example, a transmission type is used.
The recording medium will be described with reference to FIG. 2. Each of the light transmissive substrates 11 and 12 made of, for example, a glass material, and the photoreactive property formed between the light transmissive substrates 11 and 12. And a hologram recording layer 15 made of a monomer.
The thickness of the hologram recording layer 15 is set to, for example, 0.3 to 2.0 mm, preferably 0.5 to 1.0 mm, from the viewpoint of recording / reproducing capability.

  The hologram recording method may be either transmissive recording or reflective recording. In the following, a case where a hologram is recorded by reflection type recording will be described as an example.

FIG. 1 is a time chart for explaining an example of the hologram recording / reproducing method of the present invention.
When recording a hologram, first, a pre-cure is performed on the recording medium (T0). Pre-curing can be performed, for example, by irradiating the entire surface of the recording / reproducing area of the recording medium with light from a laser light source or LED light source that emits laser light having the same wavelength as the hologram recording / reproducing light source. The time required for the pre-curing is, for example, 200 ms.

In hologram recording, a plurality of holograms formed by causing signal light and spherical reference light to interfere with each other in a state where the recording medium is stationary with respect to a unit recording / reproducing area of the recording medium is obtained by spherical reference light. The incident direction to the recording medium is changed and overwritten at the same location on the recording medium, thereby recording a multi-hologram in which a plurality of holograms are overwritten at the same location (T1). Here, the irradiation time t of recording / reproducing light (signal light and spherical reference light) for recording one hologram is, for example, about 1 ms.
The unit recording / reproducing area in the recording medium is, for example, a disc-shaped recording medium, in which the recording / reproducing area on the surface of the recording medium is divided into a plurality of recording / reproducing parts arranged in the circumferential direction of the recording medium. Each block can be set to a block unit obtained by further dividing each block into a plurality of block units arranged in the radial direction from the center of the recording medium toward the outer peripheral edge. Further, in a card-like recording medium, each of a plurality of recording tracks extending in one direction is formed so as to be aligned in a direction perpendicular to the one direction at a predetermined pitch, and the recording track or a sector in the recording track is a unit. It can be set as a recording / playback area.

After a multi-hologram consisting of a predetermined number of holograms is recorded, one of the optical head and the recording medium provided with the recording / reproducing light irradiation optical system is relatively unidirectional along the surface of the recording medium with respect to the other. Micro-movement (shift) is performed (T2). Here, the moving speed of the optical head and the recording medium is such a magnitude that vibration is not generated, and is a magnitude that moves a distance of 10 μm in a time of 50 ms, for example.
In this state, a new multi-hologram is recorded in a state where a part of the recording area overlaps the recording area of the already recorded multi-hologram (T3).

  By repeating such an operation, a shift multiplex hologram sequence in which a plurality of multi-holograms are recorded so as to be aligned in the one direction with a part of the recording area overlapping each other is recorded.

  For example, as shown in FIG. 2, the hologram is recorded by the signal light Ls generated by separating the light emitted from the recording / reproducing light source (not shown) from one side of the recording medium 10. The light is condensed by the lens 35 and applied to the recording medium 10. On the other hand, the reference light generated by separating the light emitted from the same recording / reproducing light source as the signal light Ls is incident on the reference light focusing objective lens 40 via the reference light incident angle changing means 45, It is converted into a spherical wave by the reference light condensing objective lens 40 and irradiated to the recording medium 10 from the other surface side of the recording medium 10 as reference light (spherical reference light) Lr. Thereby, in the recording medium 10, the interference fringes by the signal light Ls and the spherical reference light Lr are recorded as a hologram. Here, one hologram has a substantially circular shape in plan view, and the size thereof is, for example, 500 μm in diameter.

  In the recording of the multi-hologram, the reference light condensing objective lens 40 is controlled by controlling the operation of the reference light incident angle changing means 45 in a state where the position of the irradiation area of the signal light on the recording medium 10 is fixed. The incident direction of the spherical reference light Lr irradiated via the recording medium 10 is changed, whereby a new hologram is recorded at the same location as the already recorded hologram.

As the reference light incident angle changing means 45, an acousto-optic element is preferably used. As the acoustooptic device, for example, an acoustooptic modulator (AOM) can be used.
In the acousto-optic modulator, for example, the incident direction of the reference light can be changed by controlling the signal frequency for amplitude modulation of the carrier wave that drives the acousto-optic modulator, so that the hologram can be recorded and reproduced at high speed. Become.

The operation principle of the acousto-optic modulator will be described. As shown in FIG. 3, in the acousto-optic modulator, an ultrasonic wave U is generated when the frequency-modulated driving input signal S is given from the outside, and the super As the sound wave U is propagated to the acoustooptic medium 46, the density of the periodic refractive index is formed in the acoustooptic medium 46. When the light Lr ′ for reference light is incident on the acousto-optic modulator, carrier wave diffracted light, lower side band diffracted light and upper side band diffracted light corresponding to the frequency of the drive input signal S are generated. In the invention, for example, the lower sideband diffracted lights S _{L1 to} S _Ln are used as light for reference light. In this case, unused carrier diffracted light and upper band diffracted light are shielded by a shielding plate (not shown). Reference numeral 41 in FIG. 3 denotes a lens that constitutes a relay lens together with the spherical reference light focusing objective lens 40.

Therefore, in the acousto-optic modulator, the frequency of the driving input signal S is controlled, so that the reference light collecting objective lens for the lower sideband diffracted light beams S _{L1 to} S _Ln as shown in FIG. Since the incident position at 40 is changed, the incident direction of the spherical reference light Lr with respect to the signal light can be changed. In FIG. 4, P1, P2,..., Pn indicate the incident positions of the lower sideband diffracted lights S _{L1 to} S _Ln . The white arrows shown in FIGS. 3 and 4 indicate the direction of change of the incident positions of the lower sideband diffracted lights S _{L1 to} S _Ln by changing the frequency high.
The drive control method for the acousto-optic modulator is not limited to such a method.

  In the recording of the shift multiplex hologram sequence, as described above, one of the optical head and the recording medium is slightly moved (shifted) in one direction along the surface of the recording medium relative to the other. As described above, the moving speed of the optical head or the recording medium is set so as not to cause vibration in the optical head or the recording medium.

In the hologram recording / reproducing method of the present invention, for example, in each block unit (unit recording area) of a disk-shaped recording medium, a plurality of tracks each extending in the radial direction of the recording medium are positioned so as to be spaced apart in the circumferential direction. A plurality of shift multiplexed hologram sequences are recorded on each track. When the number of holographic recordings in one unit recording area is saturated, post-cure is performed on the recording medium.
Post-cure can be performed by irradiating the entire surface of the recording / reproducing area of the recording medium with light from a laser light source or LED light source that emits laser light having the same wavelength as that of the hologram recording / reproducing light source, as with pre-cure. .
Similarly, for example, in a card-like recording medium, post-cure is performed on the recording medium when the number of multiplexed recordings of holograms in one unit recording area is saturated.

  As described above, in the hologram recording / reproducing method of the present invention, the product of the angular interval θ [°] for changing the incident angle of the spherical reference light and the shift amount δ [μm] of the optical head or the recording medium is α [ [° · μm], it is preferable that the angle interval θ and the shift amount δ are set so that 50 ≦ α ≦ 100. When the value of α is within the above numerical range, it is possible to increase the density of information recorded on the recording medium without causing crosstalk. On the other hand, if the value of α is less than 50, it will be difficult to separate and reproduce the holograms related to adjacent multi-holograms, as will be described later. On the other hand, when the value of α exceeds 100, the recording density of information on the recording medium decreases.

The angle interval θ is preferably set within a range of 1 ° to 10 °, and the shift amount δ is preferably set within a range of 5 μm to 50 μm.
As a specific example, when the shift amount δ is set to 10 μm, for example, the angle interval θ is set within a range of 5 ° to 10 °, and in particular, the angle interval θ is set to 5 ° (α = 50), for example. Setting is preferable because the recording density can be increased as much as possible. At this time, when a reference light condensing objective lens having a numerical aperture NA of, for example, 0.85 is used, a hologram that can be overwritten at the same location without causing crosstalk is used. The number (number of overwriting) can be 16. Further, when the shift amount δ is set to 40 μm and the angle interval θ is set to 1.25 ° (α = 50), the number of holograms that can be overwritten in the same place without causing crosstalk (( The number of overwriting) can be 64.
Further, for example, when a reference light condensing lens having a numerical aperture NA of 0.6 is used, if the shift amount δ is set to 10 μm, for example, overwriting is performed at the same location without causing crosstalk. The number of holograms (number of overwriting) that can be performed is six.

  In the hologram recording / reproducing method of the present invention, data information relating to the hologram recorded by irradiating the spherical reference light is reproduced. That is, as shown in FIG. 2, the reproduction light emitted from each hologram related to the multi-hologram toward the other surface of the recording medium 10 by irradiating the recording medium 10 on which the hologram is formed with the spherical reference light Lr. Lg travels backward in the optical path of the light for reference light from the polarizing prism beam splitter 42 to the recording medium 10 via the reference light focusing objective lens 40 and enters the polarizing prism beam splitter 42. Since the reproduction light Lg is rotated by 90 ° with respect to the polarization plane of the reference light, the reproduction light Lg passes through the polarizing prism beam splitter 42 and enters the image sensor 50. When the reproduction light Lg is detected by the image sensor 50, the data information related to each hologram in the multi-hologram is reproduced independently.

Here, in the case of performing multiplex recording of holograms by the angle multiplex method that is preferably used conventionally, the angular interval θ is set to about 0.1 °, for example, and a plurality of holograms are placed at the same location on the recording medium. Multiple holograms are recorded by multiple recording. However, in such a multiplex recording of holograms, when recording a new multi-hologram, the new multi-hologram must be recorded at a position sufficiently separated from the recording position of the already recorded multi-hologram. In fact, it is difficult to record a plurality of multi-holograms in a state where the recording areas partially overlap each other as in the present invention.
However, in the multi-hologram shift-multiplexed hologram sequence recorded with the angle interval θ and the shift amount δ set as described above, the reference light used for reproducing the hologram is a spherical wave. Therefore, as shown in FIG. 5, the reproduction lights Lg1 and Lg2 of the plurality of holograms multiplex-recorded at the same location are emitted in different directions and are incident on the image sensor 50. Thereby, the reproduced images I1 and I2 of the plurality of holograms reproduced at the same time are reproduced in a state of being separated in the image sensor. In addition, when spherical reference light is irradiated in a state where the Bragg diffraction condition is satisfied in one multi-hologram, each hologram in the other multi-hologram does not satisfy the black diffraction condition. Such a hologram cannot be reproduced.
In FIG. 5, kr1 and kr2 indicate the wave number vectors of the spherical reference light irradiated at different incident angles, and kg1 and kg2 indicate the recording grating vectors of the two holograms recorded at the same location.

  Hereinafter, a specific example of a hologram recording / reproducing apparatus in which the above-described hologram recording / reproducing method of the present invention is executed will be described with reference to the drawings.

FIG. 6 is an explanatory diagram showing an outline of the configuration of an example of the hologram recording / reproducing apparatus of the present invention together with a recording medium.
The hologram recording / reproducing apparatus includes an optical head including a recording / reproducing light irradiation optical system that irradiates, for example, a disk-shaped recording medium 10a with signal light Ls and spherical reference light Lr, and a recording medium 10a in a plane along the surface thereof. And a recording medium driving mechanism (not shown) for rotating (rotating) and translating.

  The recording / reproducing light irradiation optical system divides the light from the recording / reproducing light source 21 composed of, for example, a blue laser light source, and the light for signal light and the light for reference light, for example, from a polarizing prism beam splitter. A light separating means 25, a signal light irradiating optical system for generating the signal light Ls from the signal light, and irradiating the recording medium 10a with the signal light Ls from one surface side of the recording medium 10a, and a reference light A spherical reference light irradiation optical system that converts light into spherical reference light Lr and irradiates the recording medium 10a from the other side of the recording medium 10a, and a reproduction light detection optical system that detects reproduction light from the hologram. I have. A beam shaping prism 22 is disposed on the optical path of the laser light between the recording / reproducing light source 21 and the light separating means 25.

  The signal light irradiation optical system modulates the beam expander 26 that expands the beam diameter of the signal light from the light separation means 25 and spatial information corresponding to the page data to be recorded with the signal light. A spatial light modulator (SLM) 30 that emits light with its polarization direction (polarization plane) rotated by 90 °, and a Nyquist filter 32 that adjusts the frequency band in the Fourier plane of the light modulated by the spatial light modulator 30; The relay lens 31 for causing the light modulated by the spatial light modulator 30 to enter the Nyquist filter 32, and the signal light that condenses the light emitted from the relay lens 31 as the signal light Ls and irradiates the recording medium 10a. And a condensing objective lens 35. 27 is a spatial filter having a pinhole, and has a function of removing spatial noise of signal light. Reference numeral 28 denotes a polarizing prism beam splitter that reflects the signal light incident through the beam expander 26 to enter the spatial light modulator 30 and transmits the light emitted from the spatial light modulator 30. .

  The spherical reference light irradiation optical system converts the reference light from the light separating means 25 into a spherical wave, condenses it as spherical reference light Lr, and irradiates the recording medium 10a with a reference light condensing objective lens 40. Reference light incident angle changing means 45 is provided for changing the incident position of the reference light to the reference light focusing objective lens 40 to change the incident direction of the spherical reference light Lr to the recording medium 10a. In FIG. 6, reference numeral 43 denotes a reflection mirror that reflects the reference light and changes the traveling direction of the reference light, and 44 causes the reference light to enter the reference light incident angle changing unit 45. It is a lens for.

  The reference light incident angle changing means 45 in this example is composed of, for example, an acousto-optic modulator. For example, the reference light incident angle changing unit 45 controls the signal frequency for amplitude modulation of a carrier wave that drives the acousto-optic modulator. The incident direction can be changed. Since the reference light incident angle changing means 45 is constituted by an acoustooptic element such as an acoustooptic modulator, for example, the incident direction of the spherical reference light Lr without driving the optical element or the recording medium 10a by a mechanical mechanism. Therefore, the hologram can be recorded and reproduced at high speed.

The reproduction light detection optical system includes an image sensor 50 made of, for example, a CCD.
In this hologram recording / reproducing apparatus, the reproduction light emitted from the hologram recorded on the recording medium 10a toward the other surface of the recording medium 10a is recorded from the polarizing prism beam splitter 42 via the reference light collecting objective lens 40. The light path of the reference light traveling toward the medium 10 a travels backward and enters the polarizing prism beam splitter 42. Since the reproduction light is rotated by 90 ° with respect to the polarization plane of the reproduction reference light, it passes through the polarization prism beam splitter 42. Therefore, the image sensor 50 is disposed at a position where the reproduction light from the hologram is incident after passing through the polarizing prism beam splitter 42.

The optical head in this hologram recording / reproducing apparatus includes a laser light source or LED light source that emits pre-cure and post-cure light having a wavelength different from that of the hologram recording / reproduction light source.
Such a light source 60 can be arranged, for example, so that pre-cure and post-cure light is incident on the deflection beam splitter 28 in the signal light irradiation optical system. For example, when the pre-cure and post-cure light is incident on the deflection beam splitter 28 in the signal light irradiation optical system, the pre-cure and post-cure light is transmitted through the deflection beam splitter 28. The recording medium 10a is irradiated through the same optical path as the signal light.

In this hologram recording / reproducing apparatus, the laser light emitted from the recording / reproducing light source 21 is split by the light separating means 25 into signal light and reference light. The signal light is incident on the polarizing prism beam splitter 28 via the beam expander 26. The signal light is transmitted through the polarizing prism beam splitter 28 and is incident on the spatial light modulator 30. The spatial light modulator 30 modulates the signal light into a data pattern whose polarization plane is changed by 90 °. The signal light modulated by the spatial light modulator 30 is reflected by the polarizing prism beam splitter 28 and emitted. The signal light from the polarizing prism beam splitter 28 is incident on the Nyquist filter 32 by the relay lens 31, and the spatial frequency band is adjusted by the Nyquist filter 32 to generate the signal light Ls. The signal light Ls emitted from the relay lens 31 is condensed by the signal light condensing lens 35 and irradiated to the recording medium 10a from one surface side of the recording medium 10a.
On the other hand, the light for reference light is reflected by the reflecting mirror 43 to change the traveling direction, and enters the reference light incident angle changing means 45 through the lens 44. In the state where the incident position of the reference light light with respect to the reference light focusing objective lens 40 is controlled by the action of the reference light incident angle changing means 45, the reference light light passes through the deflecting prism beam splitter 42. The light enters the reference light condensing objective lens 40. The reference light is converted into a spherical wave by the reference light condensing objective lens 40, and is irradiated onto the recording medium 10a as the spherical reference light Lr from the other surface side of the recording medium 10a. Thereby, in the recording medium 10a, the interference fringes by the signal light Ls and the spherical reference light Lr are recorded as a hologram.

  Then, in a state where the recording medium 10a is stationary, the above-described hologram recording is repeatedly performed with the incident direction of the spherical reference light Lr being changed, so that a plurality of holograms have a predetermined number of overwriting at the same location in the recording medium 10a. Is overwritten. That is, while the operation of the reference light incident angle changing unit 45 is controlled, the incident direction of the spherical reference light Lr irradiated from the reference light collecting objective lens 40 with respect to the recording medium 10a is changed at an angular interval of a predetermined size. By irradiating the signal light Ls and the spherical reference light Lr, a multi-hologram in which a plurality of holograms are overwritten at the same location is recorded.

  Next, in a plane along the surface of the recording medium 10a, for example, the recording medium 10a is finely moved (shifted) by a predetermined shift amount in one axial direction relative to the optical head. By repeating the operation of recording the hologram, a shift multiplex hologram sequence in which a plurality of multi-holograms are recorded so as to be aligned in the one-axis direction with a part of the recording area overlapping each other is recorded.

  In this hologram recording / reproducing apparatus, such an operation is repeatedly performed for each unit recording area set in the recording medium. Access to the unit recording area is performed by biaxial movement and rotation (rotation) of the recording medium 10a in addition to access by movement of the optical head.

  When reproducing data information relating to the hologram recorded on the recording medium 10a, only the spherical reference light Lr is irradiated onto the recording medium 10a. Thus, the reproduction light emitted from the hologram is detected by the image sensor 50, whereby the data information recorded in the hologram is reproduced independently.

  In the above, the embodiment in which the disk-shaped recording medium is used has been described. However, as shown in FIG. 7, the recording medium may be configured to use a disk-shaped recording medium.

The optical head in this example has the same configuration as the optical head shown in FIG. In FIG. 7, the same components as those of the hologram recording / reproducing apparatus having the configuration shown in FIG. 6 are denoted by the same reference numerals for the sake of convenience, and description thereof will be omitted.
This hologram recording / reproducing apparatus translates the recording medium 10b in two directions, ie, a direction along the track and a direction parallel to the track in the recording medium 10b in a plane along the surface of the card-like recording medium 10b. The moving mechanism 65 is provided.

In this hologram recording / reproducing apparatus, a shift multiplex hologram sequence is recorded for each sector in the recording medium 10b. Specifically, the hologram is recorded by irradiating the signal light Ls and the spherical reference light Lr to one sector in a predetermined track in the recording medium 10b. Then, in a state where the recording medium 10b is stationary, a new hologram is repeatedly recorded on the sector by changing the incident direction of the spherical reference light Lr at an angular interval of a predetermined size. A multi-hologram in which a plurality of holograms are overwritten at the same location with a predetermined number of overwriting is recorded. Next, the recording medium 10b is finely moved (shifted) by a predetermined shift amount in one axial direction along the track, and in this state, an operation of recording a new multi-hologram is repeatedly performed, whereby a plurality of multi-holograms are formed. The shift multiplex hologram sequence arranged in the one-axis direction is recorded in a state where the recording areas partially overlap each other.
Access to each sector (unit recording area) in the recording medium 10b is performed by biaxial movement of the recording medium 10b in addition to access by movement of the optical head.

  As described above, in the hologram recording / reproducing method of the present invention and the hologram recording / reproducing apparatus in which the hologram recording / reproducing method is implemented, a plurality of holograms are overwritten at the same place with the incident angle of the reference light being changed. After the multi-hologram has been recorded, the multi-hologram has already been recorded in a part of the recording area in a state where one of the recording media 10a, 10b and the optical head is shifted in one direction relative to the other. The multi-hologram recording is performed in a state of overlapping with the multi-hologram recording area. For this reason, for example, it is possible to multiplex-record holograms while suppressing the number of stop-and-go operations of the moving mechanism for shifting the recording media 10a and 10b as much as possible. Therefore, according to the present invention, a sufficiently high transfer speed can be obtained even when shift multiplex recording is performed by shifting the optical head or the recording media 10a and 10b at a moving speed that does not cause vibration. And high-speed recording / reproduction is possible.

  Further, for example, when the incident direction of the spherical reference light Lr with respect to the recording media 10a and 10b is changed by the reference light incident angle changing means 45 made of an acousto-optic element, the mechanical mechanism such as movement of the recording media 10a and 10b is driven. Accordingly, the control of the incident direction of the spherical reference light Lr with respect to the signal light Ls can be reliably performed in an extremely short time, and the configuration of the hologram recording / reproducing optical system can be simplified.

  In an apparatus in which the above hologram recording / reproducing method is executed, for example, the time required to record one hologram on the recording media 10a, 10b is, for example, 1 ms, and the number of overwritten holograms at the same location is 10, If the shift amount δ is, for example, 10 μm, and the moving speed of the recording media 10a, 10b is, for example, a distance for moving the distance of 10 μm in 50 ms, the time required for one multi-hologram recording sequence is, for example, 60 ms. Therefore, the transfer rate during recording can be 80 Mbps or more, for example, 90 Mbps.

  Furthermore, the magnitude of the product α [° · μm] of the angle interval θ [°] for changing the incident angle of the spherical reference light Lr and the shift amount δ [μm] of the optical head or the recording media 10a and 10b is 50. As described above, by setting the size of the angle interval θ and the size of the shift amount δ so as to be values in the range of 100 or less, recording is performed on the recording media 10a and 10b without causing crosstalk. It is possible to increase the density of information.

DESCRIPTION OF SYMBOLS 10 Recording medium 10a Recording medium 10b Recording medium 11 Light transmissive substrate 12 Light transmissive substrate 15 Hologram recording layer 21 Recording / reproducing light source 22 Beam shaping prism 25 Light separating means 26 Beam expander 27 Spatial filter 28 Polarizing prism beam splitter 30 Space Optical modulator (SLM)
DESCRIPTION OF SYMBOLS 31 Relay lens 32 Nyquist filter 35 Signal light condensing objective lens 40 Reference light condensing objective lens 41 Lens 42 Deflection prism beam splitter 43 Reflection mirror 44 Lens 45 Reference light incident angle change means 46 Acoustooptic medium 50 Imaging element 60 Precure And post-cure light source 65 Recording medium moving mechanism I1, I2 Reproduced image kg1, kg2 Recording grating vector kr1, kr2 Wave number vector of spherical reference light Lg Reconstructed light Lg1, Lg2 Reproduced light Lr Reference light Lr ′ Light for reference light Ls signal light S drive input signal S _{L1 to} S _Ln lower sideband diffracted light U ultrasonic wave

Claims (8)

A hologram formed by causing the signal light carrying the data information and the reference light to interfere with each other is multiplexed and recorded on the recording medium by the shift multiplex method, and the hologram is irradiated with the reference light on the recording medium on which the hologram is recorded. In a hologram recording / reproducing method for reproducing recorded data information,
Use spherical wave as reference light,
After recording a multi-hologram by changing the incident direction of the reference light with respect to the recording medium by the reference light incident angle changing means and performing multiplex recording at the same location on the recording medium while the recording medium is stationary ,
In a state where one of the optical head that irradiates the signal light and the reference light and one of the recording media is shifted in one direction relative to the other, a part of the recording area of the multi-hologram has already been recorded. A hologram recording / reproducing method, wherein recording is performed in a state of overlapping a recording area of a multi-hologram.   2. The hologram recording / reproducing method according to claim 1, wherein an acousto-optic element is used as the reference light incident angle changing means.   When the product of the angle interval θ [°] for changing the incident angle of the reference light and the shift amount δ [μm] of the optical head or the recording medium is α [° · μm], 50 ≦ α ≦ 100 The hologram recording / reproducing method according to claim 1 or 2, wherein the magnitude of the angular interval θ and the magnitude of the shift amount δ are set so as to satisfy.   4. The hologram recording / reproducing according to claim 3, wherein the angular interval θ is set within a range of 1 ° to 10 °, and the shift amount δ is set within a range of 5 μm to 50 μm. Method. A hologram formed by causing the signal light carrying the data information and the reference light to interfere with each other is multiplexed and recorded on the recording medium by the shift multiplex method, and the hologram is irradiated with the reference light on the recording medium on which the hologram is recorded. In a hologram recording / reproducing apparatus for reproducing recorded data information,
An optical head including a signal light irradiation optical system for irradiating the recording medium with signal light and a reference light irradiation optical system for irradiating the recording medium with spherical reference light;
The reference light irradiation optical system includes reference light incident angle changing means for changing the incident direction of the spherical reference light to the recording medium,
In a state where the recording medium is stationary, a plurality of holograms are multiplexed and recorded at the same location on the recording medium by changing the incident direction of the spherical reference light to the recording medium by the reference light incident angle changing means. After being recorded
In a state where one of the optical head and the recording medium is shifted in one direction relative to the other, a new multi-hologram overlaps with a multi-hologram recording area in which a part of the recording area has already been recorded The hologram recording / reproducing apparatus characterized by the above.   6. The hologram recording / reproducing apparatus according to claim 5, wherein the reference light incident angle changing means includes an acousto-optic element.   When the product of the angle interval θ [°] for changing the incident angle of the reference light and the shift amount δ [μm] of the optical head or the recording medium is α [° · μm], 50 ≦ α ≦ 100 7. The hologram recording / reproducing apparatus according to claim 5, wherein the angular interval θ and the shift amount δ are set so as to be equal to each other. 8. The hologram recording / reproducing apparatus according to claim 7, wherein the angular interval θ is set within a range of 1 ° to 10 °, and the shift amount δ is set within a range of 5 μm to 50 μm.

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